It is not clear if panic disorder (PD) and agoraphobia are variants of the same disorder or distinct diseases. A laboratory test could help resolve this issue. Research has shown that levels of the urinary lysosomal enzyme N-acetyl-beta-glusosaminidase (NAG) differ between patients with various psychiatric disorders. This study examined whether NAG levels would be similar in PD and agoraphobia, suggesting the two disorders may be the same disorder, or different, suggesting they may be distinct diseases. Differences found could suggest either qualitative or quantitative distinctions between these disorders. Ninety-one agoraphobics were compared to 24 patients with panic disorder. NAG levels were significantly lower in panic patients compared to agoraphobic patients 9.7+/- 8 versus 22+/- 21; P< .005. These data provide limited support for the hypothesis that PD and agoraphobia may be distinct diseases.